1. Field of the Invention
The present invention relates to compressors and more particularly to discharge valves for a compressor such as a hermetic compressor using carbon dioxide as the working fluid.
2. Description of the Related Art
A wide variety of working fluids have been used with compressor mechanisms. Well known refrigerants that have been widely used in refrigeration and air conditioning equipment include clorofluorocarbons (CFCs) and hydrochlorofluorocarbon (HCFC). Carbon dioxide has also been used as the working fluid in refrigeration and air conditioning systems. The use of carbon dioxide as the working fluid can provide environmental and cost advantages but requires higher compression pressures which can present various operational challenges not found with more conventional refrigerants.
The higher pressures required by carbon dioxide impacts the performance of the discharge valve used to control the discharge of compressed working fluid from a compressor mechanism. The ability of the discharge valve to resist the stress caused by repeated movement and collision with the valve seat is a key characteristic that determines the performance of the valve. Compressors using carbon dioxide as the working fluid may operate at pressures up to 2000 psi and the pressure difference on opposite sides of the valve may be 5 to 10 times the typical pressure difference when using a conventional HCFC refrigerant. Using a two stage compressor mechanism wherein one compression mechanism compresses the vapor from a suction pressure to an intermediate pressure and a second compression mechanism compresses the vapor from the intermediate pressure to a final pressure may help to reduce the loads placed upon the discharge valve. Even when a two-stage compressor is used, however, the relatively high pressures required when using carbon dioxide as the working fluid will often be damaging to a conventional discharge valve having a leaf or reed valve construction. It is also known to use a spring to bias a spherical (ball) or semispherical shaped valve into engagement with the valve seat to provide a discharge valve for a compressor operating under severe conditions. A separate retaining element is typically used to secure the spring. Such valves, however, can be difficult or time consuming to assemble due to their multiple parts and may also present durability concerns. For these reasons, an improved discharge valve construction is desirable.